Free-piston compressor



Dec. 25, 1956 Filed Feb. 18, 1952 E. A. wAcHsMUTH FREE-PISTON COMPRESSOR 2 Sheets-Sheet l 2 Sheets-Sheet 2 E. A. WACHSMUTH FREE-PISTON COMPRESSOR Dec. 25, 1956 Filed Feb. 18, 1952 5R/CH Q. wc/SMUTH y A@ Aww' ilovzwfg.

United States Patent "O FREE-PISTON COMPRESSOR Erich Anton Wachsmuth, Frankfurt am Main Fechenheim, Germany Application February 18, 1952, Serial No. 272,019 Claims priority, application Germany March 28, 1951 Claims. (Cl. 23d- 56) This invention relates to two-cylinder, free-piston enginecompressor assemblages, and more particularly to such engine-compressors in which the engines are of the internal combustion (e. g. diesel) type and the assemblage of twin construction.

From a principal aspect, the invention is characterized by an arrangement of two opposed-piston systems, having their axes parallel and working in counter-stroke relation to each other (i. e. each making its particular strokes while the other is `making its opposite strokes), the counter-stroke relation being eiected and maintained by arrangements, such as double-armed rockers (levers pivoted .between their ends) connecting the pistons in pairs, and said coupling arrangements being synchronized by suitable means, such as, advantageously, but without limitation thereto, mutually engaged toothed segments.

In a preferred embodiment, in 'which two motor-compressor systems work in counter-stroke relation, the energy required to effect compression in .one motor `cylinderis lfurnished directly from the energy produced during the working .stroke in the` corresponding cylinder.` Accordingly, there will not be required, with such a construction, the measuresheretofore functionally necessary with familiar free-piston machines for the pneumatic accumulation of energy for performing the work of compression in the motor-fparticularly the large clearance volume of the compressorcylinder, ras well also as cushioningspaces (accnmulators)k for the storage of energy, which characterize freepiston machines. Thereby, machines constructed in accordance with the invention obtain an unusually favorable u ratio, for, a free-piston machine, between suction stroke` `and stroke-volume, whereby the already favorable cost of construction of knownfree-piston machines is still further improved.` By the elimination of special pneumatic cushioning means, particularly the thermodynamic, butalso the mechanical, eti'lcienoyfa thicker diagram is obtained): is improved andthereby thejeconomyeofrsuch machines.

The two motor-compressor systemsof a machine con, structedg: according to an illustrative embodiment of the present invention, considered individually, are very similar intheir construction torconventional `free-piston compressors.` nCentrally.between the compressor cylinders,

which lie to the outside, and axially in line with thecom-` pressor cylinders,.lies the motor cylinder, which isvopen at both ends. A,Two diierential pistonswhose smallpiston portions are associatedwitlnthe motor cylinder and whose largerpiston portionsare associated withthe compressor 'I cylinders, convert, without the intermediation of any special .transmissiom the workof the motor of each system into the. work of compression.` In contrast with conventional` constructions, in which the energy necessary to etfect compression in the motor must be secured from the'energyiprovided by the reexpansion of the'air remaining in the clearance volume ofthe compressor (by reason of which fact the clearance volume must "bel maintained lsubst'antiallyflarger V,than 'is customary and ldesirable in 2,775,398 Patented Dec. 25, 1956 ICC ordinary compressors), with the foregoing constructionas a result of the double-armed rocker coupling or the like-the work done during the outward stroke in one cylinder always and directly furnishes the energy needed for the compression of the charge in the other. Thus, there is here eliminated the necessity of a pneumatic accumulation of energy' to 'provide for the work of compression in the motor.

Furthermore, with a free-piston engine constructed according to the present invention, the ratio between the working stroke and the stroke-volume can be maintained of the same order of magnitude as with normal crank compressors. From this there results also a considerable improvement in overall eiciency in comparison withthe usual `crankshaft arrangements, compared with which,`

as many experiments conrm, the conventional free-piston machine, despite elimination of the crank transmission, is no better.

In the accompanying drawings, in which for purposes of illustration two illustrative embodiments of the invention are shown:

Fig. l is a diagrammatic View, in central longitudinal section, with parts in elevation, through a motor-compressor in which the invention is incorporated.

Fig. 2 isa similar View, with parts omitted, of a somewhat modiied motor-compressor in which the invention is incorporated.

Fig. 3 is a transverse section on the line 3-3 of Fig. 2, with parts not essential to the disclosure of the present invention omitted. y

Referring to the drawings, and rst to Figure 1, it will be noted that motor cylinders 1, 1 are provided. The axes of these cylinders are at least substantially parallel and they are;'supported by a frame F. In the motor cyl-l inders` 1,1 there reciprocate in counter-stroke relation to each other two pistons 4, 5 and 4, 5 which control the scavenging'slots 2, 2 and the exhaust slots 3, 3. These four pistons, formed as diiferential pistons, are coupled in pairs (4 coupled with 4', and 5 coupled with 5') each pair by a double-armed rocker 6, 7 (otherwise stated, centrally pivoted levers), the first pair by the rocker 6, the second by the rocker 7, so that the outward travel (working stroke) of the pistons associated with the cylinder 1 corresponds with the inward (compression) stroke of the corresponding pistons in the cylinder 1', andvice versa. The two double-armed rockers 6 and 7 pivoted respectively at 8 and 9, carry fixed` to them, toothed segments 10 and 11 which swing in the' same direction as engaged with each other at a common plane which cuts the central portions of the power or motor cylinders 1, 1 and is perpendicular to the axes of said cylinders. The rockers 6, 7 have their pivots closer to each other than the distance between the` relatively remote ends of the compressor cylinders and have connections with the motor-compressor piston units with which they are respectively connected betweenthe remote ends of the pistons of such piston units. t

Each of the pistons, 44 `and 5, 5 supports for rocking movement therein a transverse pin P, and these pins have Vguideways 4P, 4P, SP and SP in them respectively.` Eachrocker 6, 7, `is provided at its opposite ends with aportion (such portions severally designated 6a, 6a' and 7a, 79) slidably received in one of the guideways 4P, 4P, 5P, 51. v

Compressor cylinders 12, 13 and 12', 13 are disposed coaxial with the motor cylinders 1, 1 and are open at bitter/ends by eylinder hearts i4, l and 14', .1.5' whieh carry` the suction vand discharge valvesV 16, 17.v

Two receivers 18 are sho`vvn. Beyond the discharge Valves 17 there are ebnneetetinressnreeretaning valves t2., one arranged between eeehl tiiseharge valve .and a reeeiver 1.8,- These Pressnrenetainins valve-.s .rnav he renleeed by a single pressure retainingvalve if. .a `4suitable eenduit arrangement is providedY These pressure retainins valves, that isr spring-leaded valves, which permit the air tb enter the reeeiver 18 enlv when it exeeeds the designed (rated) pressure of the compressor, are necessary with the. niaehine operating Without the possibility of energy storage, in order to enable the machine to be satisfaettirily started and maintained .in Operation independent of the pressure in the receiver. 'i Immediately befere starting the unit, the .spaces 2.1 between the dis.- chargle valve and the pressure-.maintaining valve, which spaces. are eonneeted with eaeh ether through. an equalizatien, line 20, are, fer example by tneans or a small hand pump, pllnined. np. t0- the ratedrressnra so that at the compressor Iside normal operating conditions are already Bresent when the. tirst stroke ef. the niaehine takes. place.

hetnet starting siesirabiy is eiieetedv through the sheeting apart of the pistons 4, S which have been brought t ogether inte their extreme inner positions in the startint7 cylinder 1. A small cartridge, provided with a small powder charge, and readily inserted in a suitable chamber 2.2, eernrnnnieatins with the spacey 23 between the pistons of the motor cylinder 1, when said pistons are in their most closely adjacent positions, serves to eiect the shooting, the powder charge4 of the cartridge being ignited by a spring bolt striking nnen. its perensslve. can The. energyof the powder charge is so determined that it shall be equal to theA energy which is available during full load operation for forcing the pistons. apart. The pistons 4 and 5,- driven outwardly by the powder gases, therennen previste, as in normal operation, the energy needed. fer etteetins eeninresslon in the cylinder 1.' and, the neeessarv nsefnl werk, in. that they e-.ernpress the air Whieh was siiehetl inte the eernptessor. evlinders 1.2. and. 1.3. nnen movement. nf. the- Pistens in the eylinrler 1 to.-` Wettii each. ether Prier te starting an@ three. the eens Pressed sir ent Upon the 'overrun ins et the. exhaust sind. inlet. Slbts 3' 2i in the Starting. e ...intier 1.,. that eylinder is scavenged and. chargedr asv during D Qrural operation, and. sirnnltaneenslv. the nennst eharge of combustible. rniirtnre is inieetee into the eennter-eylinder 1.', which has. been exhansteft by the inetien. transnted troni. the roeleert. and, nnen the. ignition. et this mixture., the, normal. running condition of the rneter is; attained- Fianres 2 and. 3v show a nrorlitied. design of motoreeniliressbr. and. the. Inndiiieatiens. Whieh. are sisniiieant in eenneetien with the present. invention are.v the. only Ones Whieh need. be. speeiiieallv mentioned.- lt willhe, Observed that a Pair of motor VCylinders. 3.1i andn 31; are. arranged with. their axes parallel and.l that. inthe cylinder 31 there reciprocate the motor portions of pistons 3 4 and 35. while inthe evlintier 3.1 the. motor; portions. nf other pistons. 34.' and 35 are reeiproeable.- The pistons are again. differential pistons andthev are Connected. for movement in counter-stroke relation in pairs, 34, 34 and 35 35', as will shortly be described.v Theconnections include double-armed rockers 3.6 and 37 which pivot on axes 38 and 39 respectively. The doublefarrned wehe. are ebnstrneted with. their atrns separate. and mounted upon and keyedv against relative rotation with respect to a shaft 40 oscillatablly supported inA a framek F'. Keys K fix the relation of the arms to the shafts.l

Considering the construction 'oft the rocker- 37 (they are similarly constructed) it will be noted` thatthis is made up of an upper (as shown in thedrawing) arm 41 and a lower arm 42, and between the hubs 41Jn andvv 4.2.11 of. these atnis there isA arranged. the. hub.y portion. 43 et ann 44;. which entries.. atits. ...r end ataek` seg.-

4 s which. interensases with. eeasit facing rack segment associated with the rocker 36. The

4 hubs of the arms 41, 42 and 44 are secured together by bolts 45.

The outer ends -of the arms 41 and 42 are designated 51 and 52, and the hubs 41h and 42h are oset from the planes of the outer ends 51, 52 of the arms 41 and 42, -so that they may have the hub portion 43 of the arm 44 mounted between them and still have the outer ends 51, 52 of the arms in the central longitudinal planes of the cylinders 31 and 31'. The outer ends of each arm are provided with bearings 54 surrounding pins 55 which are in turn supported in box elements 56 which are slidably arranged in guides 57 extending transversely to the several pistons and providing for guided movement of the boxes 56 transversely of the pistons as the latter reciprocate. It will be evident that as in the first construction described, the pairs of pistons will be maintained in synchronism and thc pistons 34, 35 will operate in counter-stroke relation with the pistons 34, 35 and the explanations of the advantages of the arrangement of Fig. l will all be applicable to the embodiment disclosed in Fig-s. 2 and 3.

The specific structural elements described, including the double-armed rockers and toothed segments for the coupling and synchronization of the piston systems selected for description are but representative of other constructional features which may be employed in the practice of the invention, which is not confined to the singlestage construction of compressor herein described, but alsol includes multi-stage compressors of the same type.

While there are in this application specically described two forms which the invention mayassume in practice, it will be understood that these are shown for pur-poses of illustration, and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What is claimed is:

1. Two-cylinder, free-piston compressor, characterized by the arrangement of two opposed-piston systems arranged with their axes substantially parallel and working in counter-stroke, whose operation in counter-stroke is effected by coupling ararngements in the form of doublearmed rockers oscillating on fixed axes and connecting the pistons in pairs, which coupling arrangements are synchronized by mutually engaged toothed segments one xed ot each rocker and each directly engaged with the other.

2. In combination, two two-piston, free-piston compressors having their axial lines substantially parallel, and means for eifecting operation of the pistons of said compressors in counter-stroke relation and maintaining synchronism between them including a pair of doublearmed rockers connecting the pistons of said systems in pairs, said double-armed rockers having mutually engaged toothed' segments secured to them and having the arcs of their respectiveV pitch circles struck from the axes of` rocker oscillation and their mesh line in a plane midway between said. rockers and perpendicular to the axial lines of saidl compressors.

3. In an internal combustion, free-piston motorcom pressor, in combination, coaxial motor and compressor cylinders respectively containing motor and compressor pistons which form a pair, other coaxial motor and compressor cylinders containing` other motor and compressor pistons which form anotherpair, said' rst mentioned motor and. enrnpresser cylinders arranged. with their axes. parallel to. the axes of. said second mentionedmotor. and. com.- pressor cylinders, and means. for connecting the piston pairs. contained in said first and second mentioned coaxial motor and compressor cylinders, to causev them to move inY ennnterestrokerelation te, eaehA other including a. lever nivotabie npona. fixed.. aaisbetween-theiey1indersin which saldi eorrespendins. Pisten pairs.. are.Y contained, said. axis beingy disposed., between. the ends... of said cylinders and said lever Vhaving its opposite ends slidably and pivotally connected with said piston pairs at points between` the opposite ends of each vof thelatter.` l. c 4, Amotor-compressor as denedin claim 3, in which eacli end of said lever has a slidingl `and rocking connection with a piston pair alternatelytransmitting movement to and deriving movement from the latter, and said piston pairs being hollow and housing said connections in their respective interiors. .p

5.` A motor-compressor of the type described comprising. in combination two power cylinders disposed side by side and each having at each of its opposite ends a cornpressor cylinder, `two pairs of opposed motor pistons, one pair reciprocable in each .of said powe'r cylinders, a compressor piston movable with each motor piston and reciprocable in a compressor cylinder, two levers pivoted on iixed axes and .each operatively connected at one end with a motor piston and a compressor piston, and means arranged wholly between the `most widely spaced points in said compressor cylinders for connecting said levers to swing mutually oppositely with respect to each other, in synchronism, said last mentioned means comprising arms, one connected to each lever adjacent the center of the latter, and arcuate racks one on each of said arms meshing directly with each other.

6. A motor-compressor comprising motor and compressor cylinders, pairs of pistons adapted to reciprocate in said cylinders, and means connecting said pairs of pistons to force the pistons of one pair to approach each other as those of the other pair move apart including a pair of rockers and arcuate gear means rocking with said rockers and engaged with each other, said rockers and said arcuate gear means rocking therewith rocking on stationary axes of which the distance apart is equal to the diameter of the pitch circle of either of said arcuate gear means.

7. In a motor-compressor consisting of at least two opposed-piston motor compressor units each having motor and compressor pistons and motor and compressor cylinders, means connecting the pistons of said units in such a manner that, on its working stroke, the motor piston of each unit moves its own compressor piston to etlect compression and simultaneously causes the compression stroke of the corresponding motor piston and the suction stroke of the corresponding compressor piston of the other unit, said connecting means including rockers swingable on iixed axes in planes perpendicular to the axes of said cylinders and at least substantially midway between the ends of the strokes of the pistons which they connect, and means in the space between said connecting means connecting the latter whereby the motor and compressor pistons at the opposite ends of each unit are maintained in synchronism with each other.

8. In a motor-compressor as defined in claim 7, the arrangement in which the means in the space between the connecting means connecting the latter comprises arcuate members swinging at like angular rates with the rockers and disposed in a zone transverse to said motorcompressor adjacent the longitudinal center thereof.

9. A motor-compressor of the type described comprising, in combination, two power cylinders arranged parallel with each other and with their central portions cut by a common plane perpendicular to their axes, two pairs of opposed motor pistons adapted to reciprocate in said cylinders respectively, each motor piston having xed to its outer end a compressor piston, two pairs of compressor cylinders each pair having between its cylinders one of the iirst mentioned cylinders and adapted to receive the compressor pistons xed to the outer ends of the pistons of the rst mentioned cylinders respectively, means for connecting one motor piston of one pair to the correl spending motor piston of the other pair to cause them to move simultaneously in mutually opposite directions, means for connecting the other motor piston of said one pair with the corresponding motor piston of said other pair to cause them to move simultaneously in mutually opposite directions, and `means including `elements each movable; relative tol the other and mutually'engaging with each other at said common plane for connecting said connecting means to cause the pistons of each pair to move in synchronism with each other.

10. A motor-compressor of the type described comprising, in combination, first aligned motor and compressor cylinders, second aligned motor and compressor cylinders arranged parallel to the first cylinders, a piston structure including 'motor and compressor pistons reciprocable in said rst motor and compressor cylinders, a piston structure including motor and compressor pistons reciprocable in said second motor and Vcompressor cylinders, a doublearmed rocker. pivoted on a stationary axis midway between said iirst and said second motor and compressor cylinders, and connections between each arm of said rocker and one of said piston structures including slidable and rockable connections between them.

l1. A motor-compressor ofthe type described comprising, in combination, irst aligned'motor and compressor cylinders, second 4aligned motor and compressor cylinders arranged parallel to the irst cylinders, a piston Structure including motor and compressor pistons reciprocable in said irst mot'or and compressor cylinders, a piston structure including motor and compressor pistons reciprocable in said second motor and compressor cylinders, a doublearmed rocker pivoted on an axis between said iirst and said second motor and compressor cylinders, and connections between each arm of said rocker and one of said piston structures including a block guided on said piston structure for sliding movement transverse to the axis of said structure and a pivotal connection between said block and said arm.

12. A motor-compressor of the type described comprisf ing, in combination, iirst aligned motor and compressor cylinders, second aligned motor and compressor cylinders arranged parallel to the iirst cylinders, a piston structure including motor and compressor pistons reciprocable in said rst motor and compressor cylinders, a piston structure including motor and compressor pistons reciprocable in said second motor and compressor cylinders, a double-armed rocker pivoted on an axis between said rst and said second motor and compressor cylinders, and connections between each arm of said rocker and one of said piston structures including an element having a sliding connection with one of said rocker arm and piston structure and a rocking connection with the other.

13. A motor-compressor of the type described comprising in combination two power cylinders disposed side by side and each having at each of its opposite ends a compressor cylinder, two pairs of opposed motor pistons, one pair reciprocable in each of said power cylinders, a compressor piston movable with each motor piston and reciprocable in a compressor cylinder, two levers pivoted on fixed axes and each operatively connected at one end with a motor piston and a compressor piston, and means arranged wholly between the most widely spaced points in said compressor cylinders for connecting said levers to swing mutually oppositely with respect to each other, in synchronism, said last mentioned means comprising arms, one connected to each lever adjacent the center of the latter and each having at its end remote from its lever a connection with the other comprising directly engaged elements between which a connection is maintained during swinging of said levers.

14. A motor-compressor of the type described comprising, in combination, two power cylinders arranged parallel with each other and with their central portions cut by a common plane perpendicular to their axes, two pairs of opposed motor pistons adapted to reciprocate in said cylinders respectively, each motor piston having xed to its outer end a compressor piston which forms therewith a motor-compressor piston unit, whereby there are two pairs of motor-compressor piston units, two pairs of compressor cylinders each pair having between its cylinders zkrses 7 oneof the rstmentioned cylinders and adapted 'to receve theeompr'e'ssor pistons xed to outer ends of the PSI'ODS' Cf the l'St mentioned CYlinderS respectively, llil for connecting one motor-compressor piston unit of one pair to the corresponding motor-compressor piston unit of the other pair to causefthem to move simultaneously in mutually opposite directions, said means including a rocker pivoted betweenl its ends and having connections with the vmntor-compressor piston units between the remote ends of the pistons of the latter, means for connecting the'other motor-compressor piston unit of said one pair with the 'corresponding motor-compressor piston unit of said other pair to cause them to move simultaneously in mutually opposite directions, said last mentioned means including a rocker pivoted between its ends and having connections with the motor-compressor piston units between the remote ends of the pistons of the latter, and means for connecting said connecting means to cause the motorcompressor piston units of each pair to move in synchronism with each other, said rockers having their pivots closer to each other than the relatively remote ends of the compressor cylinders.

15. In a motor-compressor consisting of at least two opposed-piston motor-compressor units each having motor and compressor pistons and motor and compressor cylin- 8 ders, means connecting the pistons of said units in sutzh akmanner that, on its Working stroke, each motor piston of 'e Unit nves its'` Wn Compressor pistn to effect compression and simult'nously causes the compression stroke of thecerr'esp-onding motor piston and the sueT tion stroke of the corresponding compressor piston of theoth'er unit, said connecting means including rockers swingable on ixed axes in planes perpendicular to the axes of said cylinders and between the remote ends of the strokes of the pistons which they connect, and means bridging the space between said connecting means connecting the latter whereby the motor and compressor pistons at the opposite ends of each unit are maintained in synchronism with each other.

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